Weapons with positive chamber locking are designed such that on firing the cocked gun, the bolt locks the rear part of the chamber, preventing the rupturing of the cartridge case that might otherwise result from the pressure developed by the combustion gases.
Generally, weapons with positive chamber locking are constructed to withstand pressures of 50%-60% beyond the design pressure of the relevant ammunition.
There are some instances where the pressure reaches a level of double or more the design pressure. This may be the result of blockage of the barrel due to the projectile, or in consequence of dampness or some foreign body, for example. Such a consequence may also result from use of an unsuitable propellant, or from too large a charge, i.e. too much propellant.
In these occurrences the high pressure which develops may seriously damage the weapon and may also injure the shooter or bystanders.
After activating the primer, the propellant is ignited. The burning of the propellant releases prodigious amounts of gases developing high pressures within the chamber of the gun. The high pressures which develop are isostatic, i.e. the pressure is applied equally in all directions. The bolt supports the base of the cartridge case and prevents it from deforming outwards as a result of the pressure exerted by the expanding gases. The radial pressure exerted by the gases released from the propellant forces the sides of the cartridge casing outwards and against the walls of the chamber (breech). By virtue of the retaining force applied on the cartridge casing by the walls of the chamber, the casing does not explode. The pressure generated drives the projectile down the barrel in the direction of the muzzle, allowing the conflagration gases released to expand lowering the pressure within the chamber. The cartridge case is then expelled from the breech with the help of the extractor hook.
The hook of the extractor mechanism constitutes a weak point in the wall of the chamber where the casing is not supported inflexibly. Often, the outward pressure acting on the wall of the chamber deforms the insufficiently supported cartridge casing outwards at this point, and the pressure causes the head of the extractor to be pushed outwards. This outwards movement of the extractor head allows the casing to continue to stretch under the pressure of the expanding gases, and it may rupture. The outbreak of gases in this area and the asymmetric distortion cause damage to the rifle receiver and other internal parts. Also, distorted cartridge cases may not be extracted properly and are a key cause of jamming of the firing mechanism. In extreme cases the damage may be severe enough to render the rifle unserviceable.
The present invention is directed to preventing or at least minimizing the likelihood of such failures.